Aircraft main engines not only provide propulsion for the aircraft, but in many instances may also be used to drive various other rotating components such as, for example, generators and pumps. The main engines may also be used to supply compressed air to the aircraft's environmental control system, which may be used to supply temperature-controlled air to both the aircraft cabin and to electronic equipment within the aircraft.
When an aircraft is on the ground and its main engines are not being used, an alternative power source may be used to supply electrical power to onboard electrical equipment, such as the aircraft avionics suite. In addition, during some ground support operations, an external supply of cooling or heating air may be used to supply temperature-controlled air to the cabin and the onboard aircraft electrical equipment. For some type of aircraft ground support applications, most notably military aircraft ground support applications, a ground power cart may be used to supply electrical power and temperature-controlled air to the onboard electronic equipment and the aircraft cabin.
One particular ground power cart that may be used during aircraft ground support operations includes an auxiliary power unit (APU) that generates and supplies electrical power to onboard electrical equipment, and supplies high temperature (e.g., ≧300° F.) compressed air to an air conditioner module. The air conditioner module conditions the compressed air to a predetermined temperature and supplies the conditioned compressed air to the aircraft. The air conditioner module may be used in at least two modes, a cooling mode, to supply cool air, or a heating mode, to supply warm air. To do so, the air conditioner module may include a primary heat exchanger, a condenser, a moisture separator, and one or more cooling turbines. Typically, this air conditioner module is designed so that when it is operating in the cooling mode it will supply cool air at a specified flow rate and at a predetermined desired temperature for a given, predetermined design ambient temperature and design electrical load. For example, the module may be designed to supply cooling air at 100 lb/min, and at a temperature no higher than 55° F. when the ambient temperature is 125° F. and when a specified maximum electrical load on the aircraft is energized.
When actual ambient temperature is below the design ambient temperature, the air conditioner module may supply cooling air at the 100 lb/min flow rate and at a temperature that is less than 55° F. In some instances, supplying air to an aircraft at a flow rate of 100 lb/min and at a temperature less than 55° F. may not be desirable. In addition, when the actual electrical load being supplied by the APU is below the design electrical load, it may not be needed or desirable, to supply a flow rate of 100 lb/min of cooling air, either above or below 55° F. Nonetheless, current ground power carts are typically configured to supply the full rate of cooling air flow without regard to the ambient temperature or supplied electrical load. Consistently supplying cooling air at such a relatively high flow rate can adversely impact the lifetime of the APU or air conditioner module components. This can also result in increased fuel consumption by the APU.
Hence, there is a need for a system and method of providing temperature-controlled air to an aircraft environmental control system and electrical power to onboard aircraft electrical loads during ground support operations that can increase system component lifetimes, and/or can result in reduced fuel consumption. The present invention addresses one or more of these needs.